Every turbine engine has an optimum fuel to air ratio for starting and operating the turbine engine. It is common practice to use fuel scheduling cams for controlling the fuel flow to the turbine engine.
In order to start such turbine engines an operator moves a power lever from a cut-off position, where fuel communication to the turbine engine is interrupted, to a start position. As the compressor of the turbine engine is rotated, a feedback signal is supplied to a metering valve which schedules a fuel to the engine at a predetermined fuel to air ratio corresponding to engine speed to start the engine. This type of feedback control is adequate when the turbine engine is operating at or substantially near atmospheric pressure and sea level.
Because of the power which such turbine engines produce they are often used on aircraft which require substantially instantaneous maneuverability. Unfortunately, such aircraft are often required to fly at high altitudes and under conditions wherein smoke or other contaminates are often encountered. If the smoke or contaminates reduce the percentage of oxygen in the air supplied to the compressor sufficiently, the fuel to air ratio is upset and complete combustion of the fuel supplied to the turbine does not occur which can result in a "flame out". Thereafter, it is imperative that the fuel supplied to the turbine be interrupted to prevent damaging the turbine engine. Thus, the pilot must move the power lever to the cut-off off position to terminate the flow of fuel to the turbine. Thereafter, the pilot must restart the turbine engine while the aircraft is in the air. To restart the turbine engine, the pilot moves the power lever to an idle position. With the power lever in the idle position a starter rotates the air compressor. As the compressor rotates, a feedback apparatus controls the scheduling of the fuel to the turbine at a fixed fuel to air ratio corresponding to sea level. Unfortunately, at such an altitude, the time required to start the turbine is different than at sea level. Thus, restarting of the engine can often result in a delay in the power operation of the aircraft.